Polyvinyl chloride (PVC) is widely used in both its rigid and flexible forms in such applications as films, siding, sheets, pipe and tubing. Because rigid PVC is a hard, brittle thermoplastic polymer, it is often mixed with a modifier to form a composition that is less prone to failure on impact. Known PVC modifiers include polyacrylic resins, butadiene-containing polymers such as methacrylate butadiene styrene terpolymers (MBS), and chlorinated polyethylene (CPE) resins. For example, in U.S. Pat. Nos. 3,006,889 and 3,209,055 the use of a broad range of chlorinated and chlorosulfonated polyethylenes in blends with PVC is disclosed. These modifiers form small rubbery microdomains when mixed in PVC compositions that improve the impact resistance of these compositions.
Hydrocarbon rubbers such as ethylene/alpha-olefin copolymers have advantages over the aforementioned modifiers in that they are low density, have excellent stability at PVC processing temperatures (e.g. 170-210° C.) and are UV resistant. For example, in U.S. Pat. No. 5,925,703 Betso et al. teach the use of linear ethylene/alpha-olefins to improve impact performance of filled thermoplastic compositions, including polyvinyl chlorides. However, the use of these hydrocarbon rubbers as impact modifiers for rigid PVC applications has been hampered by the fact that the small rubbery microdomains have not formed in the size range for effective impact modification when the hydrocarbon rubbers are mixed in PVC compounds.
More recently, impact modifiers that are mixtures containing chlorinated polyethylenes and other polymers have been disclosed. As an example, Aono et al., in Japanese Published Patent Application No. 7-11085, disclose the use of a mixture of a chlorinated polyethylene prepared from a polyethylene of molecular weight 50,000 to 400,000 and AES resin (acrylonitrile-EPDM-styrene), optionally in combination with other polymers, as an impact modifier for PVC. Further, in U.S. Pat. No. 6,124,406 Cinadr et al. teach that blocky chlorinated polyethylenes can be used to compatibilize hydrocarbon rubber and PVC to give a PVC composition with improved impact resistance. The Cinadr patent also teaches that randomly chlorinated polyethylenes, such as Tyrin® chlorinated polyethylene, are ineffective as compatibilizers due to poor interfacial adhesion between the PVC and hydrocarbon rubber. The Cinadr patent teaches PVC compositions containing 0.5-10 parts wt. of the blocky chlorinated polyethylene and 1-10 pts.wt. of a polyolefin elastomer per 100 pts.wt. of PVC. Similarly, Mitsubishi Kasei Vinyl KK in Japanese Published Patent Application No. 2-45543, disclose vinyl chloride resin compositions containing 1-10 parts wt. of a chlorinated polyethylene and 1-10 pts.wt. of an ethylene/alpha-olefin copolymer per 100 parts of the vinyl chloride resin.